1. Field of the Invention
The invention relates to communication networks. In particular, the invention relates to novel and improved connection admission control for a communications network comprising nodes connected by links.
2. Description of the Related Art
A communication network comprises nodes connected by links. A node refers to a network element implementing a protocol used for communicating with other nodes. A link refers to a communication facility or medium over which nodes can communicate. A communication network may either be connectionless such as an IP-based (Internet Protocol) network, or connection-oriented such as a fixed telephone network. When a traffic flow comprising data packets is transmitted from a given ingress node to a given egress node, there are often multiple different routes available via various nodes and links between the ingress and egress node. These routes are referred to as paths. In the following the term path is used to refer specifically to a loop-free path.
Different paths have different costs associated with them. For example, a given path may have higher delay than another path. Thus it is advantageous to determine these costs beforehand and select a path based on this information. Since a traffic flow comprising packets may be distributed via multiple paths simultaneously, more than one paths may also be selected.
The process of determining costs and selecting paths is often referred to as load distribution. Load in this context refers to the amount of packets or bytes being transferred over nodes and links thus loading them. Distributing traffic flows over multiple paths in a communication network has several advantages, such as fast failure recovery due to pre-existence of multiple available paths between source and destination, higher throughput for a given infrastructure and reduced packet delay. Load distribution may be static, in which case assignment of jobs to hosts is done probabilistically or deterministically, without consideration of runtime events. Alternatively load distribution may be dynamic, in which case it is designed to overcome problems of unknown or uncharacteriseable workloads, non-pervasive scheduling  and runtime variation, i.e. any situation where availability of hosts, composition of workload or interaction of human beings can alter resource requirements or availability. Dynamic load distribution systems typically monitor workload and hosts for any factors that may affect the choice of the most appropriate assignment and distribute jobs accordingly. Prior art load distribution includes application U.S. Ser. No. 10/286,477 of Heiner, Balandin, filed Nov. 1, 2002, which is commonly assigned with the present application. The disclosure of this application is incorporated by reference herein. U.S. Ser. No. 10/286,477 relates to a dynamic load distributing method and system using local state information.
Today more and more networks optionally guarantee a certain level of Quality of Service (QoS) to a user or a traffic flow associated with the user. For example, user downloading a video stream may have been guaranteed a certain minimum bandwidth to allow the video stream to download without interruptions.
In order to allow this guarantee of a minimum Quality of Service, a technique known as Connection Admission Control (CAC) has been developed. Connection Admission Control involves admitting a new traffic flow to a network only, if the Quality of Service requirements of the new traffic flow as well as the already existing traffic flows can be maintained. Otherwise the new traffic flow is rejected.
Prior art Connection Admission Control techniques typically involve counting the traffic admitted to the network so far, or measuring the traffic loads in the network. The measurements are then used to decide whether to admit a new traffic flow or not.
Furthermore, prior art Connection Admission Control techniques are typically centralized in the sense that there is a central entity in the network which knows the load state of the whole network and which decides whether to admit a new traffic flow or not. As a consequence, a significant amount of signaling is required in order to keep the central entity up-to-date on the load state of the whole network.
Prior art centralized Connection Admission Control techniques include techniques with single-path routing, techniques with multi-path forwarding, and various combinations thereof. Furthermore, prior art includes polling the load over the complete ingress-egress path with predefined alternative paths.
A global approach, that is, measuring the load via polling the complete path, is common to these prior art techniques. However, the network wide polling has major disadvantages. Most importantly, with multiple ingress nodes all ingress-egress nodes have to be synchronized so that they all have a similar view of the network. Otherwise, route flaps will occur. Furthermore, the network wide polling requires accurate traffic models which are difficult to provide.
Therefore, the object of the present invention is to alleviate the problems described above and to introduce a solution that allows distributed connection admission control in which only local events are monitored to decide whether to admit a new traffic flow or not.